Radio system



May 29, 1928.

R. L. DAVIS RADIO SYSTEM Filed June 10, 1925 a w m0 V L M w H WITNESSES:

ATTORN EY in the rectifier output.

Patented May 29, 1928..

uuirso STATES 1 mm PA ROBERT ll. DAVIS, OF WILKINS BURG, PENNSYLVANIA, ASSIGNOR T03 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A. CORPORATION OF PENNSYLVANIA.

v RADIO SYSTEM.

Application filed June 10,1925. Serial No. 36,101.

vide a triodevacuum tube radio signalling system, a rectifier and filter combination adapted to co-operate therewith, and keying means having auxiliary means forpreventing the development of undesirably high-potentials.

member connected across the terminals of a filter inductance whereby the latter may be short circuited.

In the prior construction and operation of radio signalling systems, it has been, found convenient to generate radio frequency currents by means of vacuum-tube oscillators, and to interrupt the oscillations by suitable keying means. For the generation of substantial amounts'of radio-frethermionic rectifier devices. Such rectifier devices, however, furnish apulsatmg cur-,

rent. which pulsations cause a modulation of the radio-frequency output. This modulation has been found objectionable for signalling systems where it is desired to use the pure heterodyne reception method.

In order to avoid such modulation, it has been found desirable to connect a filter system between the oscillation generator and the rectifier device 'to' smooth out the current pulsations Keying has been effected by making the grid of the oscillation generator more strongly negative, which may be accomplished by the application of a definite negative grid bias, or by open-circuiting a grid leak between the grid and the cathode. In either instance, the conductivity of the tube is markedly decreased very suddenly and the sudden reduction of current through the filter choke results in the development of very high instantaneous potentials.

In many instances it is not convenient to employ tubes which will withstand the excess voltages. This is especially the case I Another object of my invention is to provide a key having an auxiliary contact the front contact of which is connected to when it is desired to send pure, continuous TENT OFFICE? Wave signals instead of theinterrupted, continuous wave signals described in thep'reviously-mentioned copending application,

My invention provides means for preventing the application of ,these sudden high potent'ials'upon the oscillation generator during the operation of keying.

Other objects and structuraldetails of my invention will be apparent from the following description when read in connection With the accompanying drawing, wherein Figure 1 shows a preferred embodiment of my invention, and I I 1 Fig. 2 shows an alternative embodiment.

' Referring to the drawing,

70 an oscillation radiator comprises an aerial 1,,a tuning inductance 2, and a counterpoise 3. The radiator is connectedto anoscillation generator comprising a triode 4 connected to a local oscillatory circuit conslsting'of an ind'uctance 5 and a condensertby means of a plate circuit connection 7 a cathodeconnection 8 and a grid connection 9 through a stopping condenser 11. A grid leak 12 has one terminal connected to the grid circuit 9. A'key '14 has a bar that is connected. 7

to the cathode circuit 15 of the triode 4 and the other terminalof the gridleak12'.

A rectifier system comprises thermionic rectifiers 16 and 17 that are connected to a filament-heatingtransformer 18 and a plate currenttransformer 19'. Both transformers are supplied by a source of alternating current 21. r

A filter system is connected between the oscillation generating system and the rectifier system. This filter consists of an inductance 22"and capacitances 23, 24 and 25 connected in a well-known manner.

Referring to- Fig. 1, the output terminal of the filter inductance- 22 is connected to the cathode circu-it'15 to'whi'ch the key 14 is also connected. contact which is adapted to close simultaneously with, or slightly before, the opening of the front contact, The back contact is connected to the in-put terminal of the filter inductance 22. 3

In the operation of the sysem, the key 14 may be depressed and upon energization of the retifiers and the filament of the oscillation The key 14 has a back V terminals to the back contact of the key 14.

key may be alternately opened and closed to interrupt the trains of oscillations" into the desired signal code. With the key ladeipressed,-a suitable grid bias for satisfactory operation is developed under. the control of the grid leak 12.

Upon opening the key, the grid circuit throughthe leak 12 is opened andthe grid immediately becomes more negative to a degree sufiicient to prevent the development of oscillations by the'triode 4, and to reduce the current traversing the tube. Simultaneously, the increase in voltage which tends to occur across the terminals of the inductance 22, due to the great increase in impedance of the triode 4, isfby passed through the back suitable for small and medium powers. the event,'however, that a very high power system is employed, theenergy by-passed contact of the key 14 and, therefore, only "the normal voltage produced bythe rectifier 19 impressed upon the triode 4:. This is an unfiltered voltage with the usual fluctuation in it but, since the triodeis not oscillating, the fluctuation is not objectionable.

Upon recl'osing the key 14, the shunt is removed from the filter inductance 22 and it resumes its activity and simultaneously the from the inductance 22 through the back con- .,tact of the key 14, may be sufficiently great to cause troublesome arcing of the key contacts and it may tend to produce local lowfrequency surges. I

This may beavoided by the embodiment shown in Fig. 2, in which a resistor 26 is connectedinseries with the back contact of "the key 14 for the purpose of dissipating the energy from the inductance 22. A large condenser 27 may also be advantageouslyadded in certain instances where it isv desired to bypass ,only the inductive component of thecoil 22 and not to by-pass the current produced by the ohmic drop in ,the coil."

'In the event that still more electrical energy is to be translated in the apparatus,

the system of. Fig, 2 may prove insuflicient for complete protection of the back contact of the key 14. Additional protection to these contact members may be obtained by shunt- .ing them with a condenser in series with a suitable resistance.

In ,the event that it is desired to connect the filter inductance in the ungrounded side of the circuit, the same results as are obtained by the previously described constructions maybe ob-tamed by adding an insulated winding to the core along side of the coil of the filter inductance 22 and connecting its The closure of the contacts thus closes the circuit in the damper winding which ab;- sorbs all of the energy due to the discharge of the magnetic field in the coreof the filter inductance 22 which otherwisewould pro-' out departing from the spirit thereof, and

it is desired, therefore, that only such limitations shall be imposed thereon as are indicated by the prior art or by the appended claims. 1 r v I claim as my invention: l. A radio signalling system, comprising an oscillation generating means, a source of fluctuating current connected thereto, a filter means connected therebetween, and means for simultaneously causing the cessation of oscillations in said generator and the shortcir'cuiting of an element of said filtermeans.

2. A radio signalling system, comprising an oscillation generating means,'a source of fluctuating current connected thereto, a filter means connected therebetween, and a keying means having a back contact" member connected to said current source and a front contact member connected to said oscillation generating means;

3. A radio signalling system, comprising an oscillation generating means, a, source of energy therefor comprising an alternating current generator and a rectifier, a filter systern connected therebetween, a keying meansassociated with said generator for interrupting said oscillations, andmeans associated with said key for preventing the development of excess voltages in said filter during non-oscillating periods. I 4. A radio signalling system, comprising an oscillation generating means, an energy supply therefor comprising a dynamo and rectifier, filter means comprising an inductance, connected therebetween, and a keying means, associated with said generator, and having a back cont act member adapted to short-circuit said inductance and a front contact member connected to said oscillation generating means. I I

5; A radio signalling system, comprising a triode oscillation generator, meansfor causing the grid thereof to become sufliciently negative in potential to stop the generation' of oscillations, an inductance in the supply circuit of said generator, and means associated with said first-mentioned means for preventing the development of excess voltage in said inductance. v

6. A radio signalling system, comprising a triode oscillation generator, a plate current supply comprising a generator and rectifier device and connected thereto, filter means comprising associated inductance and capacitance elements connected therebetween, a grid condenser and grid leak connected to the grid of said triode, and a key having both front and back contact members the front contact member being connected to said grid leak and the back contact member being connected to said filter system.

7. A radio signalling system, comprising a triode oscillation generator, a plate current supply comprising a generator and rectifier device and connected thereto, filter means comprising associated inductance and capacitance elements connected therebetWeen, a

grid condenser and grid leak connected to being connected to said filter system whereby in one position, the key opens the grid leak circuit and closes a circuit in shunt to the inductance in said filter means, and in the other position, closes the grid leak circuit, and opens the shunt circuit for the filter.

Intestimony whereof, I have hereunto subscribed my name 1925.

ROBERT L. DAVIS.

this 21st day of May, 

